1. Field of the Invention
The present invention relates to a color ink-jet recording ink set, ink-jet recording method, recording unit, ink-cartridge, ink-jet recording apparatus and bleeding reduction method, to obtain color images of high density, grade, sharpness and quality by the ink-jet recording even on plain paper.
2. Related Background Art
Heretofore, in order to form a black image which is excellent in printing density, printing grade, waterproof, and lightfastness on plain paper by the ink-jet recording system. There has been proposed use of black pigment ink. Besides, there have been proposed an ink set which would not cause bleeding at the boundary between an image printed with black ink and an image printed with color ink, as well as the ink-jet recording method or apparatus using it. In Japanese Patent Application Laid-Open No. 7-145336, for example, there is described an ink set in which at least one ink is a polymer-containing anionic ink, and the bleeding is reduced by the mutual contact of the anionic ink with a cationic ink on a multicolor print element. In Japanese Patent Application Laid-Open No. 10-183046, there is described an ink set capable of reducing bleeding by combination use of a black ink containing a carbon-black pigment having a cationic group on its surface as a coloring material, and a color ink containing an anionic dye as the color material.
However, in the method as described in Japanese Patent Application Laid-Open No. 7-145336, where bleeding in multicolor printing is suppressed by mutual contact between an anionic ink and a cationic ink in the presence of a polymer, the polymer may adversely affect the ink reliability depending on the polymer type. This poor reliability means, if there is a certain time interval, one minutes, for example, between the ink ejection performance from a nozzle in recording, it may happen that the next ink droplet cannot be ejected steadily, causing disturbed printing (such a phenomenon is called xe2x80x9cpoor ejectabilityxe2x80x9d).
Besides, the method described in the above Japanese Patent Application Laid-Open No. 10-183046 uses a combination of a black ink using cationic carbon black and a color ink using an anionic dye, and the aggregates formed between the coloring materials suppress bleeding. However, with the ink-jet inks of which coloring material concentrations are not so high as to cause sufficient aggregation, there may happen, especially on the recording medium of high permeability such as normal paper, bleeding between black and color images, or a phenomenon called xe2x80x9chazexe2x80x9d in the black image. Here, haze, a whitish black region which should be solid black, is caused as the black ink is drawn deep into the recording medium by the action of highly penetrable color ink in the boundary region between a color image and a black image, when image black ink and color ink are applied in the same scan.
The inventors of the present invention have been studying the black ink containing self-dispersible carbon black as the coloring material, as a black ink which can give black images of high grade and has a stable ink composition. The present inventors have studied the use of this black ink in multicolor image formation, and found out that the excellent properties of this black ink can give high grade multicolor image. To achieve a still higher grade of multicolor image, however, it has been found that bleeding control in the boundary region between the black image and the color image is necessary. At present, there is no sufficient technical knowledge for the use of black ink containing self-dispersible carbon black as the color material for the formation of multicolor images, and decisive technique for bleeding prevention has not yet been found.
The present invention was made with such a background, and one object of the present invention is to provide an ink set for color ink-jet recording, which can sufficiently suppress bleeding in the boundary region between the black ink and the color ink when used for a color image formation, and has reliability as an ink-jet recording ink.
Another object of the present invention is to provide an ink-jet recording method capable of forming a color image high in image density and excellent in grade.
Still another object of the present invention is to provide an ink-jet recording apparatus capable of forming a high grade color image, an ink cartridge, and a recording unit.
Still another object is to provide a method for steadily and sufficiently alleviating bleeding in the boundary region between the black ink-jet image and the color ink-jet image.
According to one aspect of the present invention, there is provided an ink set for color ink-jet recording comprising a black ink and a color ink, wherein the black ink comprises a cationic self-dispersible carbon black, and the color ink comprises an anionic dye and an anionic substance.
According to another aspect of the present invention, there is provided an ink-jet recording method, comprising the steps of:
ejecting a black ink comprising a cationic self-dispersible carbon black from an orifice in response to a recording signal; and
ejecting a color ink comprising an anionic dye in response to a recording signal,
wherein the color ink further comprises an anionic substance.
According to further aspect of the present invention, there is provided a recording unit, comprising:
a first ink container containing a black ink comprising a cationic self-dispersible carbon black;
a second ink container containing a color ink comprising an anionic dye and an anionic substance; and
a head for ejecting the black ink in the first container and the color ink in the second container.
According to a still further aspect of the present invention, there is provided an ink cartridge, comprising:
a first ink container containing a black ink comprising a cationic self-dispersible carbon black; and
a second ink container containing a color ink comprising an anionic dye and an anionic substance.
According to a still further aspect of the present invention, there is provided an ink-jet recording apparatus, comprising:
a first ink container containing a black ink comprising a cationic self-dispersible carbon black;
a second ink container containing a color ink comprising an anionic dye and an anionic substance; and
a head section for ejecting the black ink and the color ink, respectively.
According to a still further aspect of the present invention, there is provided a method for alleviating bleeding in a boundary between a black image formed by an ink-jet method and a color image formed by an ink-jet method, wherein the black image is formed with a black ink comprising a cationic self-dispersible carbon black and the color image is formed with a color ink comprising an anionic dye and an anionic substance.